The Coronary Drug Project was undertaken to evaluate the efficacy of different lipid-lowering drugs in the long-term treatment of coronary heart disease and to study the natural history and clinical course of the disease. The CDP is a multi-clinic study consisting of 53 Clinical Centers, a Coordinating Center, a Central Laboratory, an ECG Reading Center, and a Drug Procurement and Distribution Center. A total of 8,341 patients were enrolled in the study during the recruitment period, Mar. 1966 through Oct. 1969. Only males between the ages of 30 and 64 having a history of at least one ECG-documented myocardial infarction, and belonging to NYHA functional class I or II were eligible for the study. Each patient was randomly assignied to one of the following six treatment groups: Mixed conjugated equine estrogens (two dosage levels), clofibrate, dextrothyroxine, nicotinic acid, and placebo. All patients are to be followed for minimum of five years on their assigned CDP medication plus a final four months off their CDP medication unless definitive results allow termination before 5 years. The information obtained from the study is being to evaluate the CDP drugs with respect to effects on mortality, cardiovascular morbidity, and serum lipids as well as side effects, biochemical effects, and electrocardiographic changes. Placebo group date on the demographic, clinical, electrocardiographic, biochemical, pharmacologic, and radiographic variables observed at baseline, as well as other aspects of the natural history and clinical course of coronary heart disease, will be analyzed for prognostic significance. Aspirin is added to the study for evaluating its effectiveness in reducing the incidence of recurrent myocardial infarction and other cardiovascular events and, in so doing, also increase life expectancy in men with evidence of previous myocardial infarction.